Secret history of the Navy SEALS: Intimate photographs that reveal life inside the world of America's most elite warriors

At the bottom of a swimming pool a group of men voluntarily sink with their hands bound behind their backs after instructed to reach their face masks on the floor using only their teeth.

There appears little struggle as the men calmly work to complete their task before the next one is issued, most likely making their challenge even harder, but all in a day's training.

These are the United States' unsung heroes, the Navy SEALS, an exclusive band of about 2,400 special operators most famously responsible for the 2011 midnight raid that led to the capture of Osama bin Laden.

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Lessons on drown proofing: Seen here a group of students with their hands tied behind their backs descend to the bottom of a pool to recover their face mask using only their teeth

Gadgets: A flying Humvee is one of the concepts in development by the US Defense Advanced Reseach Projects Agency for the SEALs

Capturing: A U.S. Navy SEAL Sniper in Iraq holds his weapon steady in a shot taken by Greg Mathieson, who has spent the last six years researching and photographing them

American Heroes: The men are said to have so many gadgets and equipment, as well as high skill levels and education that Mr Mathieson easily calls them the American James Bonds

Special Warfare: The book shows and tells all other members of special warfare as well, with there being about 20 support personnel for every Navy SEAL out there

The first Hush Puppy pistol made exclusively for the US Navy SEALs. The 9 mm pistol with sound suppressor was developed to quietly kill enemy guard dogs during night time operations

By land and by sea: Special Warfare Combatant-craft Crewman (SWCC) move though rivers at a high rate of speed in specially designed Riverine boats outfitted with heavy weapons

All work? A US Navy SEAL uses a computerized HMU underwater to take measurements of a beach landing area

Dating back: Submersible canoes are seen being launched by OSS Maritime Unit personnel during training operations in the Pacific Theater during the 1940's

Attack: Navy SEALS are seen landing during an attack on a ship in one of 931 photographs part of Mr Mathieson's new book

Night or day: A US Naval Special Warfare Combatant crewman fires a 50 caliber machine gun from Riverine boat in the darkness of night, as seen through night vision goggles

'No one's ever done a book that shows everything they do,' Mr Mathieson said. 'They only show bits and piece of them over the years but no one has ever done the entire history and this goes back to WWII, all the way up to the future.'

That future refers to outlines of new concepts and prototypes currently under development.

One such seen in his book is a drawing of the Marion Hyper-sub prototype Fathom.

It's an undersea vehicle capable of carrying up to eight personnel to depths of 600 feet while traveling 1,000 miles without having to refuel.

Some gadgets from the past he uncovered, specifically 1961 and 1962, also proved most remarkable - even if never used.

‘The most amazing was the SADM, Strategic Atomic Demolition Munition,’ he told NBC.

‘This
was a 160-pound atomic bomb that was the size of a basketball. It had
an underwater casing that SEALs would tie to their chest, jump out of
planes and then place wherever ordered.

Inventions: The Marion Hyper-sub prototype Fathom is one of many concepts and products that corporations are developing to pitch to SOCOM and the US Navy to help in fighting the new age of terrorism, drug trafficking and security

Equipment: An SDV is lifted from the indoor testing pool while the newer Advanced SEAL Delivery System (ASDS), a self contained one-atmosphere, dry combatant submersible that has a diver lock in/lock out, is prepped in the background

Morning wake-up call: Coronado beaches in California serve as the morning physical training course, where running-conditioning is done from one end of the beach to the other on the sand

Author and photographer: Greg E. Mathieson Sr. stands in a dust storm at the secluded US Navy SEAL base in Fallujah, Iraq while producing exclusive material for his newly released book

Decorated: The US Navy Congressional Medal of Honor (center) is seen with the US Navy Cross, Silver Star, Bronze Star and Purple Heart medals along with tools of US Navy SEALs (night vision, Sig Sauer pistol, body armor and dive knife)

More: Mathieson and David Gatley's new book opens with an introduction by President George W Bush and a foreword by Secretary of the Navy and 9-11 Commission member John Lehman

‘Think about it, this was long before micro-circuitry and the advances we take for granted today. It existed, but the SADM was never used,’ he said.

'I tried to start this [project] 30 years ago when I was in Honduras and I met a SEAL,' Mr Mathieson toldNBCof his project’s inspiration.

'I wrote a letter to Adm. George Worthington back then and was denied complete access. Fast forward and Adm. Worthington had retired, but we had stayed in touch. He opened doors because he saw this was a story that really should be told and with that, I had access,' he said.

Today his 403-page book opens with an introduction by President George W Bush and a foreword by Secretary of the Navy and 9-11 Commission member John Lehman.

'It took a lot of getting to know all the right people,' he admits to Fox.

'Because of unparalleled access given the author and photographers, this book has insights behind the scenes of the support personnel, unique training, underwater vehicles, operations in Iraq and Afghanistan, unique weapons developed just for the SEALs as well as into the future of Naval Special Warfare (NSW) written by Secretary of the Navy Donald Winter,' the book states.